The need has arisen for systems to protect aircraft against intrusion while they are parked at airports. While the need for security systems exists to some extent for all aircraft in all locations, the need is most acute in the case of private and business jets parked at foreign or unfamiliar airports. Security systems must protect against a variety of intrusions such as sabotage to the aircraft, placement of listening devices, smuggling, particularly of drugs, theft and acts of terrorism. To provide complete protection, the system must monitor not only entrances to the aircraft, but also access panels, engines, and wheel wells.
Aircraft security systems utilized in the past typically include a number of sensors at sensitive areas on the aircraft for detecting intrusions, and a control unit for monitoring the sensors and providing alarm indications. These systems must, of course, be reliable and have a low false alarm rate. In addition, certain requirements are unique to aircraft applications. For example, wires used to interconnect the various elements of the system must be minimized in weight and cost and must be easy to install. The installation of wire and cable in an already-completed aircraft is difficult, expensive and adds undesired weight. Accordingly, it is desirable to minimize the number of wires interconnecting the various elements. One prior art system utilizes two wires for data communication and two additional wires for carrying power to the various system elements. It is also desirable to minimize the power consumed by the system since batteries or other power supplies are typically the heaviest part of the system. An additional requirement of aircraft security systems is that RF radiation, which can interfere with aircraft communication and airport operations, be suppressed or eliminated.
A further requirement of aircraft security systems is that they maintain reliable operation over long periods of time when subjected to vibration, dirt, wide temperature variations, degradation with time, and, in the case of optical sensors, variation of ambient light conditions. Such conditions may cause sensors to stop operating without the knowledge of the aircraft personnel or may cause false alarms.
During the life of an aircraft security system, it is often desirable to change, remove or add sensors without requiring major system modifications to accommodate the altered sensor configuration.
It is a general object of the present invention to provide improved aircraft security systems and improved methods of operation for aircraft security systems.
It is another object of the present invention to provide aircraft security systems having reduced weight and which are easily installed in aircraft.
It is a further object of the present invention to provide aircraft security systems wherein power and data communication signals are carried between a central control unit and remotely-located sensor controllers on a two-wire bus.
It is still another object of the present invention to provide aircraft security systems and methods of operation which accommodate changes in sensor outputs caused by vibration, dirt, temperature variations, aging, ambient lighting, and other variable conditions.
It is yet another object of the present invention to provide aircraft security systems and methods of operations which can easily accommodate changes in sensor configurations.